Degradation Of Imidacloprid In Water And Soil By White-rot Fungi

As a representative of the first generation of neonicotinoid pesticides,imidacloprid is widely used in agricultural production activities around the world.It has the characteristics of solubility,wide applicability,and obvious pest control effects.Defects such as difficulty in self-degradation in a short time in water Imidacloprid added by foliar spraying or seed soaking in the farmland environment can easily enter the water environment such as rivers,lakes and seas due to soil leaching,soil infiltration,atmospheric deposition or water circulation,causing pollution to water bodies and thus to water bodies The growth of surrounding organisms and even human life have a negative impact and harm,and the ecological problems caused by this need to be solved urgently.Microbial technology plays an important role in the restoration of environmental pollution caused by neonicotinoid pesticides.It has attracted widespread attention due to its fast growth and breeding speed,mild reaction degree,and significant degradation efficiency.White-rot fungi,as a kind of functional fungi with high-efficiency degradation ability for difficult-to-degrade heterogeneous organic matter,has been proved to be of great significance to the degradation of organochlorine,organophosphorus,carbamate and pyrethroid pesticides.The purpose of this thesis is meant to use white-rot fungi with significant degradation ability to xenobiotic pollutants as experimental strains to study its remediation and removal effects on imidacloprid contaminated water and soil,and to investigate the cells of white-rot fungi in the process of remediation.Changes in activity,intracellular antioxidant indicators and extracellular degrading enzymes,clarify the structure and degradation pathways of the products obtained by white-rot fungi from degrading imidacloprid,evaluate the environmental biological toxicity of the degradation products,and reveal that the repair behavior of white-rot fungi on imidacloprid pollution is important changes in the microbial community;explore the behavioral mechanism of white-rot fungi degrading imidacloprid from the overall perspective,and seek an efficient,low-consumption,non-toxic way to specifically treat the environmental pollution caused by imidacloprid.The work and results of this thesis are mainly divided into the following three aspects:The first part of this study is aimed to investigate the remediation behavior and mechanism of white-rot fungi in water contaminated by imidacloprid.The most representative white-rot fungi-Phanerochaete chrysosporium was selected as the experimental strain for the removal of imidacloprid in water.The degradation efficiency,cell activity,peroxidase(POD),catalase(CAT)and lignin modification enzymes of P.chrysosporium during the degradation process were investigated..The results showed that:(1)white-rot fungi have a good degradation effect on imidacloprid in water bodies.The degradation rates of imidacloprid at initial concentrations of 2,5,and 10 mg/L reached 87.8%,92.2%,and 85.3% in 6 days,respectively..(2)The cell activity of white-rot fungi exposed to imidacloprid for a short period of time is promoted due to the hormesis effects.With the increase of exposure time,imidacloprid has an inhibitory effect on the cell activity of white-rot fungi.The addition of imidacloprid induced the increase of ROS content in white-rot fungi,and promoted the expression of CAT and POD.white-rot fungi exposed to imidacloprid for 24 h,the intracellular ROS content increased sharply.The ROS content of 5,10,20,and 50 mg/L imidacloprid treatment groups reached 120%,130%,250%,and 350% of the control group’s ROS content,respectively..(3)The addition of imidacloprid and the concentration of imidacloprid affect the secretion of ligninase(Li P)and manganese peroxidase(Mn P)by white-rot fungi,and the activity of Li P and Mn P is related to the degradation efficiency of imidacloprid.The second part analyzes the products obtained from the degradation of imidacloprid by white-rot fungi,and discusses the biological toxicity of the products.By using GC-MS technology,the structure of imidacloprid product and the structure of the reaction intermediate were analyzed,and the possible degradation pathway was speculated.The biotoxicity of imidacloprid was evaluated by the growth experiments of the Escherichia coli,Microcystis aeruginosa,Chinese cabbage and rice treated with degradation products.The results are as follows:(1)The main product of white-rot fungi degradation of IMI is 1-(6-chloro-3-pyridylmethyl)-2-imidazolone.(2)The products obtained from the degradation of imidacloprid by white-rot fungi promote the growth of E.coli and M.aeruginosa,and the growth is related to the concentration of the imidacloprid added.(3)The products obtained from the degradation of imidacloprid by white-rot fungi have no obvious biological toxicity to Chinese cabbage and rice.The third part detects the degradation effect of imidacloprid in the soil from the different inoculation forms of white-rot fungi,and monitors the change trend of soil physical and chemical properties such as p H value,soil organic matter content and soil invertase content during the process,and finally from the composition of the microbial community.From the perspective of analyzing the mechanism of the remediation behavior of white-rot fungi on imidacloprid contaminated soil.The results are as follows:(1)The different inoculation methods of white-rot fungi have different efficiencies for the removal of imidacloprid in the soil.The spore-type white-rot fungi and the free white-rot fungi have the best degradation effects on imidacloprid.(2)During the process of white-rot fungi degrading imidacloprid in the soil,soil p H,soil organic matter content and soil invertase enzyme activity all have significant changes,which are significantly related to the degradation efficiency of imidacloprid.(3)The addition of white-rot fungi will cause changes in the microbial community in the soil,but it will not damage the stability of the soil itself,but will work with indigenous microorganisms to repair soil pollution caused by imidacloprid.This paper confirms the feasibility of applying white-rot fungi to treat water and soil contaminated by imidacloprid,discusses the effect of imidacloprid concentration and white-rot fungus inoculation methods on the degradation efficiency of imidacloprid;and on this basis,investigates the effect of white-rot fungi on the degradation efficiency of imidacloprid.Changes in the physiological activity and biochemical indicators of the fungal cells infer the structure and degradation pathways of imidacloprid degradation products;finally revealed the best inoculation state for the degradation of imidacloprid pollution by white-rot fungi,and carried out the entire repair behavior from the perspective of changes in the microbial community analysis.This study provides a basis and reference for the development of microbial treatment technology for neonicotinoid pesticides,and proposes a new and highly feasible solution for the problem of pesticide residues in the environment.